Why does the Crab pulsar gradually slow down?
This nebula is the product of a supernova explosion; in this section, the blast wave has encountered an area of dense interstellar gas, creating turbulence in the wave and causing it to glow. The picture is a composite of three images taken by the Hubble Space Telescope.
The Crab pulsar, like other pulsars, gradually slows down because it is losing rotational energy. This loss of energy is significant enough that the pulsar emits radiation across the electromagnetic spectrum, including radio waves, visible light, X-rays, and gamma rays.12
This energy loss is a consequence of the pulsar's intense activity. As a rapidly spinning neutron star with an extremely strong magnetic field, the pulsar accelerates charged particles to speeds approaching the speed of light. These particles release electromagnetic radiation, which carries away energy from the system. Because the total angular momentum of an isolated system must be conserved, the emission of this energy and the associated physical processes result in a gradual decrease in the pulsar's rotational speed. This steady deceleration allows astronomers to use pulsars as highly accurate cosmic clocks.134